Most aircraft have a fuselage of cylindrical general shape. The structure of the fuselage comprises substantially circular frames disposed transversely and linked to each other by longerons.
In aircraft intended for the transport of passengers, a floor needs to be formed inside the fuselage to receive the passengers. To form such a floor, a usual solution consists of disposing a cross-member inside each frame of the fuselage structure and to form a floor on the cross-members so disposed. This floor most commonly integrates longitudinal rails which are used to form the fastening for seats intended to receive the passengers as well as various members (walls, furniture, etc.) used in creating the interior layout of the aircraft.
FIG. 1 is a very diagrammatic illustration of a transverse cross-section of an aircraft fuselage. A frame 2 of circular shape can be seen here. A cross-member 4 is mounted on the frame 2 and is adapted to participate in the formation of a floor to support the load of the passengers and of the various members adapted to be located above the floor as well as to provide the separation between a cabin adapted to receive the passengers together with the cockpit, and a lower part of the aircraft forming a hold. To reinforce the structure of the floor, tie rods 6 may be provided to support a cross-member 4.